A NonlinearHeatEquationwithTemperature-Dependent Parameters M. A. Rincon 1 , J. Límaco 2 & I-Shih Liu 1 ∗ 1 Instituto de Matemática, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil 2 Instituto de Matemática, Universidade Federal Fluminense, Niteroi, RJ, Brazil Abstract A nonlinear partial differential equation of the following form is considered: ( ) u ′ − div a(u)∇u + b(u) |∇u| 2 = 0, which arises from the heat conduction problems with strong temperature-dependent material parameters, such as mass density, specific heat and heat conductivity. Existence, uniqueness and asymptotic behavior of initial boundary value problems under appropriate assumptions on the material parameters are established. Both one-dimensional and two-dimensional cases are considered. 1 Introduction Metallic materials present a complex behavior during heat treatment processes involving phase changes. In a certain temperature range, change of temperature induces a phase transformation of metallic structure, which alters physical properties of the material. Indeed, measurements of specific heat and conductivity show a strong temperature dependence during processes such as quenching of steel. Several mathematical models, as solid mixtures and thermal-mechanical coupling, for problems of heat conduction in metallic materials have been proposed, among them, [8], [6] and [13]. In this paper, we take a simpler approach without thermal-mechanical coupling of deformations, by considering the nonlinear temperature dependence of thermal parameters as the sole effect due to those complex behaviors. The above discussion of phase transformation of metallic materials serves only as a motivation for the strong temperature-dependence of material properties. In general, thermal properties of materials do depend on the temperature, and the present formulation of heat conduction problem may be served as a mathematical model when the temperature-dependence of material parameters becomes important. More specifically, we are interested in a nonlinear heat equation with temperature-dependent material parameters, in contrast to the usual linear heat equation with constant coefficients. 2 A nonlinear heat equation Let θ(x, t) be the temperature field, then we can write the conservation of energy in the following form: where prime denotes the time derivative. ∗ E-mails: rincon@dcc.ufrj.br, juanbrj@hotmail.com.br, liu@im.ufrj.br ρ ε ′ + div q = 0, (1) 1